"Physics" question, I think...?

Question

The human heart provides about 1 to 10 watts of power to circulate blood through the body. A 9.6 volt, 2.6 amp-hour rechargeable battery is used for some cordless electric drills. For 100 percent efficient conversion of electrical energy into blood pumping work, estimate how long one of these rechargeable batteries qould last when 5 watts of power is consumed. Recall that 1 J/sec = 1 W = 1 A * 1 V

Answer 1

Power of the battery is 9.6 Volt x 1 ampere
= 9.6 joule / second.
It is given that
The battery can give energy for one hour

Energy = Power x time.

Total energy available is 9.6 {joule/ second}* 1 hour.

Energy is consumed at the rate of 5 (joule /second.)

Time available is
[9.6 {joule/ second}* 1 hour] / 5 (joule /second.)
{joule/ second} gets cancelled leaving

1.92 hour or
1 hour 55 minutes and 12 seconds.

Answer 2

By definition power P is rate of flow of energy E
P=E/t

Electrical power P is a product of voltage V and current I

so P=V I

The total charge a battery can store is the product of voltage V it can maintain during a continuous discharge of current I for a period of time t (hence is the term Ampere-hours).

The energy stored in the battery is
Power in the battery = VI = 9.6 Volts x 2.6 Amperes= 25 Watts [for 1 continuous hour] (or 25 watts x 3600 sec= 90,000 Joules or 90 kJoules)

P= E/t
t= E/P= 90,000Joules/ 5Watts= 18,000sec or 5 hours